1. Field of the Invention
The present invention relates a magnetic roller for image developing means in electrophotographic system, and more particularly to a magnetic roller of image developing means that can largely reduce the cost of the magnetic rollers body, makes magnetic pole angle more accurate, and enhances the magnetic strength.
2. Description of the Prior Art
Accordingly, the image module of a laser printer, as shown in FIG. 1, includes: a photo-sensitive drum 11, which is a drum used to generate an electrostatic latent image on its surface; a corona bar 12, which is provided in one side of the surface of said photo-sensitive drum and used to distribute induction static electricity on the surface of said photo-sensitive drum; an exposure means 13, which is provided in another end away from said photo-sensitive drum and charging roller 12, and can receive the signal from an image reader to emit laser for exposure, so that an exposure area and non-exposure area similar to the image in the image reader are formed on the surface of photo-sensitive drum; a toner cartridge device 14, which is provided in another side of photo-sensitive drum in the backward position after exposure means is operated, used to provide storage of toner; a magnetic roller 15 with its surface covered by a developing sleeve, which is provided in front end of a toner cartridge outlet close to the photo-sensitive drum. The toners inside the cartridge device 14 are attracted by magnetic force of the magnetic roller 15 and distributed on the outer surface of developing sleeve 16, after the developing sleeve 16 keeps rotating and has induction with the exposure area having static electricity on the surface of photo-sensitive drum 11, toners are then attracted to the surface of photo-sensitive drum, and then, through the photo-sensitive drum 11, toners are brought to printing area. Afterwards, the toner transferring device 17 is used to transfer toners to adhere onto the surface of papers to form an image identical to the character or figure to the printed out. Then the image is obtained.
In the image developing means of printer described above, the quality of the magnetic roller has great impact on printing quality. In the conventional magnetic roller, as shown in FIG. 2, there is provided a non-conductive roller body 21, which is made of rubber, plastic or other artificial resins. A plurality of S magnetic poles 22a, 22b, etc., and N magnetic poles 23a, 23b, etc. are formed on the roller body 21 closed to the outer circular ring separately, usually in adjacent positions. Therefore, their magnetic poles can be arranged as even poles, such as dual poles, quad poles, six poles, or eight poles, etc. A conventional approach is to insert the magnetic bars with S magnetic poles and N magnetic poles in outer side into the roller body (disclosed in U.S. Pat. Nos. 4,517,719; 6,654,582). Another approach is to mix magnetic materials with rubber, plastic or other artificial resins to form a cylinder as a whole, using an exciter to excite the roller body in pre-determined outer parts of the roller body during forming the magnetic roller, so that a plurality of S magnetic poles and N magnetic poles are formed on the surface of the roller body opposite to the exciter (as shown in U.S. Pat. No. 5,129,358).
However, whether the S magnetic pole and N magnetic pole are formed by inserting the magnetic bars into the roller body or formed with the roller body as a whole, the entire cost of the magnetic roller is very high. This is because the materials of the roller body are very expensive and the technology that makes magnetic angle, magnetic strength, and magnetism equalization fit the need of printers is sophisticated. Moreover, if S magnetic poles and N magnetic poles are formed by inserting the magnetic bars into furrows formed on the surface of the roller body, this not only brings many problems with regards to density configuration, but also causes inconvenience on assembling. The problems regarding magnetic angle, magnetic strength, and magnetism equalization in each magnetic bar still need to be solved.
If S magnetic poles and N magnetic poles are formed on the adjacent edge of the whole roller body, some magnetic dipoles (small magnets) can not be exactly allocated in the position coherent to the magnetic flux, therefore, there are still some irregularly arranged magnetic dipoles (small magnets) 24 (as shown in FIG. 3) would be distributed aside the magnetic poles (as shown in area A, B, C, D of FIG. 3) and even central part of the roller body, causing the magnetic flux of S magnetic poles and N magnetic poles to be interfered, which affects the magnetic angle and magnetism equalization of magnetic poles and decreases magnetic strength, having impact on magnetic force configuration of the whole magnetic roller, making magnetization of the roller's magnetic materials incomplete. The satisfactory printing quality cannot be achieved because toners cannot be attracted on the accurate positions.
Accordingly, the present invention has been made for solving the above-mentioned problems occurred in the prior art.